remove old installations

[Roger Pack]

> Perhaps this is terribly naive:  what about
> sudo port clean --all portname

Yes that does it.
Maybe what it could do it warn when it's doing a "dirty" installation,
so that it's clearer more quickly why something may have failed (i.e.
you see
$ port install xxx
warning: installing over a previous installation
...
fetch failed please check your log

(it's more immediately obvious *why* the fetch may have failed).

-r